Studies of Resistance to Sharka (Plum Pox) in Romanian Apricot Progenies

Sharka (Plum pox) is considered one of the most devastating diseases of stone fruits in terms of agronomic impact and economic importance. The response of several apricot hybrids was evaluated over the vegetative period of 2010 by visual monitoring of symptom development and by serological and molecular methods. After two cycles of study, all the replicates of ‘Mari de Cenad’, ‘Traian’ and ‘Tabriz’ showed sharka symptoms while the replicates of ‘Stark Early Orange’ and NJA 2 did not show any symptoms and were not ELISA-positive. The resistant progenitors (‘Stark Early Orange’, NJA17, NJA42 and NJA2) were able to transmit PPV resistance to their descendants, in agreement with previous results (DOSBA et al, 1994, MARTINEZ-GOMEZ et al, 2000; AUDERGON et al, 1994). The genetic control hypotheses for PPV resistance in apricot referenced by different authors considered the resistance allele as dominant. Romanian apricot F1 and F2 progenies evaluated were classified into two groups: susceptible to PPV and resistant to PPV. After that the most important genotypes were grafted onto infected GF 305 (considered as indicator for PPV) in greenhouse conditions. The final step is the introduction and development of the marker-assisted selection (MAS) in PPV resistance F1 and F2 progenies in apricot Romanian genotypes. DNA was isolated from all hybrids and parent genotypes. These samples will be used to implement the molecular markers for identification of genes linked to plant response to PPV infection.

Cost-Effective and Time-Efficient Molecular Assisted Selection for Ppv Resistance in Apricot Based on ParPMC2 Allele-Specific PCR

Plum pox virus (PPV) is the most important limiting factor for apricot (Prunus armeniaca L.) production worldwide, and development of resistant cultivars has been proven to be the best solution in the long-term. However, just like in other woody species, apricot breeding is highly time and space demanding, and this is particularly true for PPV resistance phenotyping. Therefore, marker-assisted selection (MAS) may be very helpful to speed up breeding programs. Tightly linked ParPMC1 and ParPMC2, meprin and TRAF-C homology (MATH)-domain-containing genes have been proposed as host susceptibility genes required for PPV infection. Contribution of additional genes to PPV resistance cannot be discarded, but all available studies undoubtedly show a strong correlation between ParPMC2-resistant alleles (ParPMC2res) and PPV resistance. The ParPMC2res allele was shown to carry a 5-bp deletion (ParPMC2-del) within the second exon that has been characterized as a molecular marker suitable for MAS (PMC2). Based on this finding, we propose here a method for PPV resistance selection in apricot by combining high-throughput DNA extraction of 384 samples in 2 working days and the allele-specific genotyping of PMC2 on agarose gel. Moreover, the PMC2 genotype has been determined by PCR or by using whole-genome sequences (WGS) in 175 apricot accessions. These results were complemented with phenotypic and/or genotypic data available in the literature to reach a total of 325 apricot accessions. As a whole, we conclude that this is a time-efficient, cost-effective and straightforward method for PPV resistance screening that can be highly useful for apricot breeding programs.

Allelic variation of simple sequence repeats markers linked to PPV resistance in Chinese apricot

Apricot is one of the oldest fruit tree crops in China and it was spread via Armenia to other areas. There are about ten species of apricot (Subg. Armeniaca Mill.) worldwide, among which nine species are native to China. Sharka disease caused by the Plum pox virus (PPV) is widely distributed in the main producing regions of apricot. In this study, linked simple sequence repeats (SSR) primers were used to detect allele variations potentially associated with PPV resistance among Chinese apricot germplasm resources, including 52 accessions belonging to Prunus armeniaca, 7 to Prunus mandshurica, 6 to Prunus sibirica, 4 to Prunus mume, 17 to other species or types. The allelic variation at loci with PPV resistance showed that these SSR markers linked to PPV resistance kept a relatively high level of diversity in Chinese apricot. The special alleles and genotypes only found in South China cultivars might reveal new PPV resistance sources. Some famous local cultivars of Chinese apricot might be considered as candidates for PPV resistance.

Inheritance of resistance to Plum pox virus in the progeny of the apricot cv. ‘Harlayne’

Natural resistance toPlum pox virus(PPV), the agent of sharka disease, is one of the most important traits of interest to stone fruit breeders, although few sources of resistance have been identified. One of the few apricot cultivars which does show resistance, ‘Harlayne’, was chosen for a study of the genetics of PPV resistance. It was crossed with three different cultivars, two susceptible (‘Vestar’ and ‘Strepet’) and one immune (‘Orangered’). Four different lines (since there was one reciprocal combination) were established and the F1 crosses were subsequently inoculated with the PPV-M and PPV-D strains by grafting infected buds. A woody indicatorPrunus persica‘GF 305’ was then also top-grafted onto the plants of three of these F1 populations. The observations of leaf symptoms and accompanying ELISA tests were performed over three, or in one case five, growing seasons and then hybrids were classified accordingly, as either resistant or susceptible. The resistant : susceptible ratios were calculated and compared with expected theoretical ratios using the χ2-test. The ratios of resistant to susceptible plants in the progeny derived from the four apricot crosses are compatible with the hypothesis of three dominant genes being responsible for PPV resistance, with ‘Harlayne’ being heterozygous for all three genes. However, the possibility that resistance is controlled by just two dominant genes can not be ruled out just yet.